  :root {
      --primary: #409eff;
      --sidebar-bg: #eaf6fb;
      --content-bg: #f8fbfd;
      --header-bg: #f4fafc;
      --table-header: #f5f5f5;
      --border: #eee;
      --btn-info: #409eff;
      --btn-danger: #f56c6c;
      --btn-warning: #f6c23e;
    }
    * { box-sizing: border-box; }
    body {
      margin: 0;
      font-family: 'Segoe UI', 'Arial', 'Microsoft YaHei', sans-serif;
      background: var(--content-bg);
      color: #333;
    }
    .layout {
      display: flex;
      min-height: 100vh;
    }
    .sidebar {
      width: 220px;
      background: var(--sidebar-bg);
      padding-top: 0;
      display: flex;
      flex-direction: column;
      align-items: stretch;
    }
    .sidebar-title {
      height: 64px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 20px;
      font-weight: bold;
      letter-spacing: 2px;
      background: var(--header-bg);
      border-bottom: 1px solid var(--border);
    }
    .sidebar-menu {
      flex: 1;
      padding: 20px 0 0 0;
    }
    .sidebar-menu a {
      display: flex;
      align-items: center;
      padding: 14px 32px;
      color: #333;
      text-decoration: none;
      font-size: 16px;
      border-left: 4px solid transparent;
      transition: background 0.2s, border-color 0.2s;
    }
    .sidebar-menu a.active,
    .sidebar-menu a:hover {
      background: #fff;
      border-left: 4px solid var(--primary);
      color: var(--primary);
      font-weight: bold;
    }
    .sidebar-logout {
      margin: 0 24px 24px 24px;
      padding: 10px 0;
      text-align: center;
      background: #fff;
      border-radius: 6px;
      cursor: pointer;
      color: #888;
      font-size: 16px;
      border: 1px solid var(--border);
      transition: color 0.2s, border 0.2s;
    }
    .sidebar-logout:hover {
      color: #f56c6c;
      border: 1px solid #f56c6c;
    }
    .main {
      flex: 1;
      display: flex;
      flex-direction: column;
      background: var(--content-bg);
    }
    .header {
      height: 64px;
      background: var(--header-bg);
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 40px 0 24px;
      border-bottom: 1px solid var(--border);
      position: relative;
    }
    .header-title {
      font-size: 20px;
      font-weight: bold;
      letter-spacing: 2px;
      color: #4682b4;
    }
    .header-user {
      font-size: 16px;
      color: #666;
    }
    .content {
      flex: 1;
      padding: 32px 32px 0 32px;
      position: relative;
    }
    /* 背景装饰 */
    .decoration-yellow, .decoration-red, .decoration-green {
      position: absolute;
      opacity: 0.18;
      z-index: 0;
      pointer-events: none;
    }
    .decoration-yellow {
      top: -24px; right: 60px;
      width: 350px; height: 120px;
      background: #ffe082;
      border-radius: 70px 180px 80px 120px;
      transform: rotate(15deg);
    }
    .decoration-red {
      left: 120px; top: 320px;
      width: 120px; height: 120px;
      background: #f44336;
      clip-path: polygon(50% 0%, 0% 100%, 100% 100%);
      border-radius: 16px;
    }
    .decoration-green {
      right: 0; bottom: 0;
      width: 340px; height: 240px;
      background: #4caf50;
      border-radius: 60px 80px 190px 140px;
      transform: rotate(-20deg);
    }
    /* 表格样式 */
    .card {
      margin: 0 auto;
      background: #fff;
      border-radius: 10px;
      box-shadow: 0 0 12px rgba(180,200,220,0.08);
      padding: 28px 24px 24px 24px;
      position: relative;
      z-index: 1;
      max-width: 100%;
      overflow-x: auto;
    }
    .actions-bar {
      display: flex;
      align-items: center;
      margin-bottom: 14px;
      gap: 12px;
    }
    .search-input {
      padding: 8px 12px;
      border: 1px solid #ddd;
      border-radius: 5px;
      font-size: 15px;
      outline: none;
      margin-right: 8px;
      background: #fafbfc;
    }
    .btn {
      padding: 6px 16px;
      border: none;
      border-radius: 5px;
      font-size: 15px;
      cursor: pointer;
      margin: 0 2px;
      transition: background 0.2s;
    }
    .btn-info { background: var(--btn-info); color: #fff; }
    .btn-danger { background: var(--btn-danger); color: #fff; }
    .btn-warning { background: var(--btn-warning); color: #fff; }
    .btn-info:hover { background: #2476d1; }
    .btn-danger:hover { background: #d94444; }
    .btn-warning:hover { background: #d39e09; }
    .table {
      width: 100%;
      border-collapse: collapse;
      margin-bottom: 0;
      background: #fff;
    }
    .table th,
    .table td {
      padding: 12px 10px;
      text-align: left;
      border-bottom: 1px solid var(--border);
      font-size: 15px;
    }
    .table th {
      background: var(--table-header);
      font-weight: bold;
      color: #666;
    }
    .table tr:last-child td {
      border-bottom: none;
    }
    /* 卡片课程 */
    .course-list {
      display: flex;
      flex-wrap: wrap;
      gap: 24px;
      margin-top: 16px;
      z-index: 1;
      position: relative;
    }
    .course-card {
      width: 280px;
      background: #fff;
      border-radius: 12px;
      box-shadow: 0 1px 6px rgba(50,120,180,0.09);
      display: flex;
      flex-direction: column;
      overflow: hidden;
      transition: box-shadow 0.2s;
    }
    .course-card:hover {
      box-shadow: 0 6px 18px rgba(60,120,180,0.18);
    }
    .course-image {
      width: 100%;
      height: 160px;
      object-fit: cover;
      background: #f5f5f5;
    }
    .course-info {
      padding: 14px 15px 10px 15px;
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }
    .course-title {
      font-weight: bold;
      font-size: 18px;
      margin-bottom: 4px;
      color: #333;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    .course-desc {
      font-size: 14px;
      color: #555;
      line-height: 1.4em;
      height: 2.8em;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    .course-small {
      font-size: 13px;
      color: #999;
    }
    .btn {
      padding: 6px 16px;
      border: none;
      border-radius: 5px;
      font-size: 15px;
      cursor: pointer;
      margin: 0 2px;
      background: #409eff;   /* 默认蓝色 */
      color: #fff;
      transition: background 0.2s;
    }
    .btn:disabled {
      background: #ccc !important;   /* 禁用时变灰 */
      color: #888 !important;
      cursor: not-allowed;
    }
       /* 模态对话框样式 */
    .modal {
      display: none; /* 默认隐藏 */
      position: fixed; /* 固定定位 */
      z-index: 1; /* 置于顶层 */
      left: 0;
      top: 0;
      width: 100%; /* 全屏宽度 */
      height: 100%; /* 全屏高度 */
      overflow: auto; /* 启用滚动 */
      background-color: rgba(0,0,0,0.4); /* 黑色半透明背景 */
    }
    .close-btn {
      color: #aaa;
      float: right;
      font-size: 28px;
      font-weight: bold;
      cursor: pointer;
    }

    .close-btn:hover,
    .close-btn:focus {
      color: black;
      text-decoration: none;
      cursor: pointer;
    }

    .modal-content {
      background-color: #fff;
      margin: 15% auto; /* 居中显示 */
      padding: 30px;
      border: 1px solid #888;
      width: 400px;
      border-radius: 10px;
      box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
    }
    /* 响应式 */
    @media (max-width: 900px) {
      .layout { flex-direction: column; }
      .sidebar { width: 100%; flex-direction: row; height: 56px; }
      .sidebar-title { display: none; }
      .sidebar-menu { display: flex; flex-direction: row; padding: 0 8px; }
      .sidebar-menu a { padding: 10px 18px; border-left: none; border-bottom: 2px solid transparent; }
      .sidebar-menu a.active, .sidebar-menu a:hover { border-bottom: 2px solid var(--primary); }
      .sidebar-logout { margin: 0 10px; }
      .main { padding-top: 0; }
      .content { padding: 16px 4vw 0 4vw; }
      .decoration-yellow, .decoration-red, .decoration-green { display: none; }
    }